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Solar absorption has long been recognised as a factor in building performance. Dark surfaces absorb more solar energy than light surfaces, which is why black tarmac becomes noticeably hotter than a concrete pavement on a sunny day. The same principle applies to buildings. A dark-coloured wall or roof will absorb more heat, while a lighter surface reflects more of the sun's energy away. This concept is particularly evident in warmer parts of the world, where white or light-coloured buildings are often used to help reduce overheating and improve comfort during hot weather.

As HEM aims to provide a more detailed representation of how homes perform in the real world, it makes sense that surface colour is now part of the calculation.

To understand the practical impact, AES has created a HEM model and tested a typical two-storey semi-detached house with all external surfaces set first to light and then to dark. The results broadly followed expectations, although the differences were smaller than many might assume.

In the model, the darker version of the property performed slightly better. The additional solar absorption reduced annual heating demand by around 1% compared to the equivalent light-coloured home. While technically an improvement, it is hardly a game-changing reduction in energy use.

The picture changes when cooling systems are introduced. In scenarios where cooling was modelled, the lighter-coloured dwelling achieved a cooling demand around 9% lower than the darker equivalent. By reflecting more solar energy, lighter surfaces helped reduce summer heat gains and lessened the burden on cooling equipment.

However, where no cooling system is present, that particular advantage disappears. If there is no active cooling to operate, there is no corresponding energy saving to be realised. In this example, that leaves the darker dwelling with a marginal overall advantage due to its slightly lower heating requirement.

What these findings demonstrate is that, for most conventional UK housing, surface colour is unlikely to become a major design driver in the immediate future. Developers do not need to start specifying dark façades purely to improve compliance performance, nor should architects abandon lighter palettes in pursuit of marginal energy gains.

The more interesting question is what happens as homes evolve and our climate continues to warm. Highly glazed properties, penthouse apartments and homes in urban environments already face greater overheating risks than traditional housing. As cooling systems become more commonplace and summer temperatures become increasingly challenging, the balance could begin to shift in favour of lighter-coloured external surfaces.

Future modelling will provide a clearer picture. While Part L compliance calculations will continue to use prescribed weather files, the wider capabilities of HEM allow energy consultants to test more extreme scenarios and better understand overheating risks under future climate conditions.

The inclusion of house colour in HEM may seem like a small detail, but it reflects a broader shift in building performance assessment. Energy modelling is becoming increasingly nuanced, accounting for factors that were previously overlooked. The colour of a house will not determine whether a scheme succeeds or fails, but it is another example of how the industry is moving towards a more realistic understanding of how buildings perform in the real world.

For now, at least, there is no urgent need to bulk-buy black masonry paint.

 For further press information, please contact David Ing at Ing Marketing on david@ing.marketing or visit www.ing.marketing